The invention relates to a valve comprising a control means having a valve spool serving for the control of fluid flows, such control means being able to be moved by the application of setting forces in relation to the valve housing in a first switching movement following a first switching direction and an second switching movement following an opposite second switching direction, and is consequently able to be positioned in different switching settings, said control means being able in the first switching movement to be shifted along a displacement path from a first switching position into a preset terminal switching position, which is preset by abutment means on the housing in which terminal position it can be held by first setting forces, which are effective in the first switching direction, and from which it can be moved by the application of second setting forces, acting in the opposite second switching direction, as part of the second switching movement.
A multi-way valve of this type is for example disclosed in the European patent publication 0 678 676 B1. Here the control means is constituted by a piston-like valve spool with an axially aligned, preceding setting piston and may be positioned by the action of a control fluid in two mutually opposite terminal switching positions. Dependent on the switching position the valve ducts are linked together with various different configurations.
One problem with all valves of this type when the control means dwells in one of the terminal switching positions for a prolonged period of time, is the static friction between the valve spool and the seals surrounding it. Particularly typical cases of the effect of such behavior occur with dwell times over 2 hours. The consequence is that the setting forces necessary for shifting the control means out of the respective terminal switching position and for switching into an other switching position increase. This again means that the resistance to switching opposing the fluid power driving forces available for actuation is increased so that the switching times increase and this may lead to functional disturbances in the loads connected with the valve. Behavior in the case of monostable or two state valves is particularly critical.
One object of the invention is to adopt measures which ensure reliable switching over of the valve even following long periods of disuse.
In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention there is at least one drive means having spring means which at the start of the first switching movement is as yet ineffective and is only tensioned during the terminal part of the first switching movement by the kinetic energy of the control means, the tension force of the spring means contributing additionally, at the start of the second switching movement, to actuating forces, produced by fluid action, for producing the second setting forces.
On switching the control means over into a terminal switching position there is accordingly firstly a switching movement of the conventional sort. However once the control means has moved along a part of the switching path toward the terminal position, the kinetic energy available at this point in time, of the configuration means causes spring means of at least one drive means to be tensioned. Thus energy is transmitted to the spring means and stored therein. The storage of energy in the spring means continues as long as the control means is held by the first setting forces acting on it in the terminal switching position. These first setting forces are as a rule fluid power setting forces and in the case of monostable valves are more particularly applied by a pneumatic spring. If now the control means is acted upon by a control for the purpose of leaving the terminal position and moving into the second switching position, initially the tension forces of the spring means will be added to its actuating forces, this being sufficient to overcome the increased static friction and to switch over the control means. Delays in switching may consequently be effectively prevented even in the case of prolonged periods of idleness of the valve.
Further advantageous developments of the invention are defined in the claims.
It is possible to provide at least one drive means containing the spring means mounted stationarily on the valve housing, the tensioning of the spring means occurring because on approaching the terminal position the moving control means strikes against an impact face drivingly connected with the spring means.
Additionally or alternatively it is possible for at least one drive means to be provided on the control means as well so that it is borne by it and is entrained during the switching movements. Such a design may as a rule be manufactured substantially more simply than one involving integration in the valve housing. This is more particularly so when the drive means is integrated in a setting piston of the control means which represents a part separate from the valve spool so that it is may be employed extremely simply instead of a conventional setting piston.
The tensioning of the spring means is preferably performed by compressing the spring means between the moving control means and the support means secured to the housing, when the control means draws close to its terminal switching position. The necessary displacement path for tensioning the spring means may in this case be extremely small and more particularly substantially less than the rest of the displacement path of switching, in which the spring means is not yet functional and is not yet compressed. This means that during the switching movement there will be sufficient time for the control means to accumulate the kinetic energy necessary for tensioning or cocking the spring means.
The impact face struck at the start of the tensioning operation and associated with the spring means is preferably on a sliding plunger as part of the drive means, such plunger being able to be adjusted and running directly in the valve housing or in the control means.
In order to obtain the desired characteristic it is convenient to provide for the spring means to be subject to a certain bias even in the non-actuated state thereof. In this respect it is possible to provide adjustment means, rendering possible a predetermined presetting of the spring means. Such presetting means furthermore render possible the compensation of manufacturing inaccuracies as regards the length of the spring means, more especially when such spring means are constituted by at least one mechanical spring. As an alternative or in addition to having at least one mechanical spring it is possible for the spring means to be also constituted by a gas spring and in this case preferably a pneumatic spring.
The drive means is preferably associated with an axially terminal region of the control means. In the case of a control means having two terminal switching positions it is possible to associate a drive means with both terminal switching positions, preferably at the two axial ends of the control means.
If the first setting forces are provided by a gas spring, preferably a pneumatic spring, for example in order to produce a monostable two-state valve, the design will preferably be such that the resilient force of the spring means at least approximately equals the first setting forces or is somewhat less than they are. It is in this manner that the first setting forces may be substantially compensated for when the control means is in the terminal switching position, by the resilient force so that the actuating forces to be provided by an operating or drive fluid essentially only have to overcome the static friction of the sealing means in order to switch over the control means out of the terminal switching position into another switching position.
Further advantageous developments and convenient forms of the invention will be understood from the following detailed descriptive disclosure of one embodiment thereof in conjunction with the accompanying drawings.